This invention relates generally to the cleaning of dishes and deals more particularly with a dishwashing machine that is useful primarily in restaurants or institutions having a need to wash large quantities of dishes.
In restaurants and institutions which serve large volumes of food, conveyor type dishwashing machines are often used for washing of dishes, glasses and silverware. In conveyor type machines, the dishes are loaded in racks which are conveyed one at a time through a washing zone and then through a rinsing zone prior to being deposited on a discharge table which holds the clean dishes. In the washing zone, heated and/or chemically treated wash water is sprayed onto the dishes to remove food particles from the dishes. In the rinsing zone, the dishes are rinsed by chemically treated (low energy) or heated water (high energy) to remove the residues from the washing operation and sanitize the dishes.
As can easily be appreciated, it is highly important for the dishes to be thoroughly cleaned. If dishes are not completely clean when served to restaurant patrons, the reputation of the restaurant can suffer considerable damage and its business can deteriorate as a consequence. As can also be easily appreciated, it is important to limit the involvement of workers in the operation of the machine, both to minimize labor costs and because poorly trained employees can damage the machine and perhaps put it out of service at an inopportune time.
The conveyor dishwashing machines that have been available in the past have suffered from a number of shortcomings, most notably in their inability to consistently achieve thorough cleaning of dishes, their inability to operate reliably without frequently breaking down or requiring maintenance, and in their relatively high operating costs which are due in large part to the need for large amounts of hot water.
Typically, the machines that have been available in the past have made use of flexible curtains and the like to provide a barrier between the wash compartment and the rinse compartment. Curtains and other types of barriers are subject to becoming coated with food deposits and other contaminants which can contaminate the dishes as they move into the rinse compartment. This can result in the dishes emerging from the machine with contaminants still on them.
Although it is common for machines to have sensors for detecting when the water level is unduly low, the sensors that have been employed in the past have not been reliable. Probes which are immersed in the water are exposed to calcium and other minerals that can build up on the probe and make it unable to accurately sense the water level. Float switches have typically used plastic floats which can be damaged by the high temperature water, the chemicals it contains, or food scraps and other debris that can be present in the water. Reed switches and other electrical switches typically require printed circuit board controls and other electronic components which are both costly and subject to attack by chlorine vapors and other chemical agents that may be in the area. All of the liquid level sensors require frequent replacement and are subject to excessive maintenance requirements. If the sensors should fail to sense an abnormally low liquid level, the consequences can be severe in that the pump and heating elements can be destroyed and necessitate costly repairs and lengthy machine down time.
Another problem is that the food scraps in the wash water can be sucked into the pump and clog it up or otherwise damage it. Even though screens and other filters are normally used to avoid this problem, operators often neglect to make sure that the filter is in place. A further problem results if racks of clean dishes are not removed promptly from the discharge table. The racks can then back up and completely fill the discharge table, and the conveyor continues to attempt to convey more racks through the machine, which can cause damage to the racks and/or the conveyor mechanism.
In order to maintain the machine in a sanitary condition, it is necessary to drain it and clean it as often as twice a day. The spray arms must be removed and cleaned, and their end caps must be removed so that the interior of each spray arm can be cleaned. Existing machines are characterized by difficulty and excessive time consumption in assembling and disassembling the spray components, and this increases the labor costs and the time the machine is out of service while being cleaned. Another problem is that the end caps of the spray arms are often lost while they are detached from the spray arms during the cleaning procedure. Again, this detracts from the efficiency of the machine because it increases the time it is unavailable for use while the end cap is being located or replaced.